1. Field of the Invention
The invention relates to a clamping device, and more particularly, to a clamping device applicable to an injection-molding machine and is combined with different driving sources to improve its torque and to drive a screw rod for generating a high clamping force.
2. Description of the Related Art
The clamping device is one of many critical parts in an injection-molding machine to ensure reliable closing of a mold. Since molten material is supplied into a mold cavity under an extreme high pressure, it is necessary to apply a sufficient clamping force to tightly close the mold to avoid flashing, molded product with flashes, or other conditions that would adversely affect the quality of the molded products.
Typically, a hydraulic injection-molding machine has two types of clamping devices, a toggle type and a direct pressure type. A fully electronic injection-molding machine is one product that has recently been actively researched and developed by injection mold manufacturers all over the world. For the fully electronic injection-molding machine, the pressure cylinder of the toggle type clamping device is substituted with a motor unit to achieve the same opening/closing of the mold as the hydraulic injection molding machine, and to acquire a higher clamping force more easily than the direct pressure type clamping device.
A screw rod in the clamping device serves to covert a rotational movement into a linear movement and vice versa. Based on the mechanical equation, it is understood that a greater input torque for the rotational movement causes a greater linear thrust to be generated by the screw rod. For the direct pressure type clamping device equipped with a motor unit and the screw rod, the power output from the motor device is smaller than the pressure cylinder. So, it is necessary to increase torsion and decrease the lead of the screw rod in order to achieve the same clamping force. Similar implementing methods have been disclosed in U.S. Pat. No. 5,266,874 and U.S. Pat. No. 6,254,371 as well as in WO02/11969.
However, a typical injection-molding machine requires a high-speed actuation during clamping, while the product injection requires a high pressure clamping force. So, to achieve the objective of high speed and high pressure using a single driving source would mean use of a large and inappropriate driving source, thereby causing energy wastage. Meanwhile, an increased torsion and a decreased lead of the screw rod results in a lower speed in terms of opening/closing of the mold, leading to an increase in molding cycle time. As a result, the power of the motor unit would have to be maximized when the clamping device of the conventional injection-molding machine is applied to achieve opening/closing the mold at a high speed with a high clamping force, further wasting cost and energy.
To improve the drawbacks associated with the clamping device of the injection-molding machine as described above, relative resolutions were proposed from an issued Taiwan Patent with a Patent No. TW00537171. The patent discloses generating power using a single low power driving source. By changing the lead of the clamping device, a large lead screw rod ensures opening/closing the mold at a high speed, and a small lead screw rod generates a high pressure clamping thrust. Since the clamping force is inversely proportional to the lead size, a larger clamping force output requires a smaller lead for the screw rod.
However, there are certain limitations in terms of processing the lead of the screw rod. Even though a high pressure clamping is achieved through the patent disclosed as above, there are still limitations posed by the lead of the screw rod when a single driving source is adopted. As a result, the clamping force can only be obtained under certain criteria. So, there are still areas that require further improvements in the prior art.
Therefore, the above-mentioned problems associated with the prior arts are resolved by providing a clamping device that progresses quickly to close the mold, and provides a sufficient clamping force for clamping the mold substantially when the contact is made to the mold, so as to improve the clamping force for the injection molding machine while saving on fabrication costs and energy.